This invention relates to a process for the production of ether(s). More particularly, the invention relates to a process for the conversion of a light olefin such as ethylene, propylene, butenes, pentenes, hexenes, heptenes, etc., and their mixtures, in a conversion unit employing an acidic zeolite as olefin conversion catalyst to produce a mixture of alcohol(s) and ether(s) and thereafter recovering the ether(s) containing at most only small amounts of co-produced alcohol(s) and water. The ether(s) are useful, inter alia, as high octane blending stocks for gasoline.
There is a need for an efficient catalytic process for manufacturing ethers from light olefins thereby augmenting the supply of high octane blending stocks for gasoline. Lower molecular weight ethers such as diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have a high blending octane number. In addition, by-product propylene from which DIPE can be made is usually available in a fuels refinery. The petrochemicals industry also produces mixtures of light olefin streams in the C.sub.2 to C.sub.7 molecular weight range and the conversion of such streams or fractions thereof to ethers can also provide products which are useful as solvents and as blending stocks for gasoline.
The catalytic hydration of olefins to provide alcohols and ethers is a well-established art and is of significant commercial importance. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,162,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,849; and, 3,989,762, among others.
Olefin hydration employing zeolite catalysts is known. As disclosed in U.S. Pat. No. 4,214,107, lower olefins, in particular, propylene, are catalytically hydrated over a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of from 1 to 12, e.g., HZSM-5 type zeolite, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product.
According to U.S. Pat. No. 4,499,313, an olefin is hydrated to the corresponding alcohol in the presence of hydrogen-type mordenite or hydrogen-type zeolite Y, each having a silica-alumina molar ratio of 20 to 500. The use of such a catalyst is said to result in higher yields of alcohol than olefin hydration processes which employ conventional solid acid catalysts. Use of the catalyst is also said to offer the advantage over ion-exchange type olefin hydration catalysts of not being restricted by the hydration temperature. Reaction conditions employed in the process include a temperature of from 50.degree.-300.degree. C., preferably 100.degree.-250.degree. C., a pressure of 5 to 200 kg/cm.sup.2 to maintain liquid phase or gas-liquid multi-phase conditions and a mole ratio of water to olefin of from 1 to 20. The reaction time can be 20 minutes to 20 hours when operating batchwise and the liquid hourly space velocity (LHSV) is usually 0.1 to 10 in the case of continuous operation.
European patent application No. 210,793 describes an olefin hydration process employing a medium pore zeolite as hydration catalyst. Specific catalysts mentioned are Theta-1, said to be preferred, ferrierite, ZSM-22, ZSM-23 and NU-10.
The reaction of light olefins with alcohols to provide ethers is also a well known type of process. According to U.S. Pat. No. 4,042,633, DIPE is prepared from isopropyl alcohol (IPA) employing montmorillonite clay catalysts, optionally in the presence of added propylene. U.S. Pat. No. 4,175,210 discloses the use of silicatungstic acid as catalyst for the reaction of olefin(s) with alcohol to provide ether(s). As disclosed in U.S. Pat. No. 4,182,914, DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cation exchange resin as catalyst. In the process for producing a gasoline blending stock described in U.S. Pat. No. 4,334,890, a mixed C.sub.4 stream containing isobutylene is reacted with aqueous ethanol to form a mixture of ethyl tertiary butyl ether and tertiary butanol. U.S. Pat. No. 4,418,219 describes the preparation of methyl tertiary-butyl ether (MTBE), a high octane blending agent for motor fuels, by reacting isobutylene and methanol in the presence of, as catalyst, boron phosphate, blue tungsten oxide or a crystalline aluminosilicate zeolite having a silica to alumina mole ratio of at least 12:1 and a Constraint Index of from 1 to about 12 as catalyst. U.S. Pat. No. 4,605,787 discloses the preparation of alkyl tert-alkyl ethers such as MTBE and methyl tert-amyl ether (MTAE) by the reaction of a primary alcohol with an olefin having a double bond on a tertiary carbon atom employing as catalyst an acidic zeolite having a constraint index of from about 1 to 12, e.g., zeolite ZSM-5, 11, 12, 23 dealuminized zeolite Y and rare earth-exchanged zeolite Y. European patent application No. 55,045 describes a process for reacting an olefin and an alcohol to provide an ether, e.g., isobutene and methanol to provide MTBE, in the presence of an acidic zeolite such as zeolite Beta, zeolites ZSM-5, 8, 11, 12, 23, 35, 43 and 48 and others, as Catalyst. Germany Patent No. 133,661 describes the reaction of isobutene and methanol to provide a mixture of products including MTBE, butanol and isobutene dimer in the presence of acidic zeolite Y as catalyst. According to Japan Patent No. 59-25345, a primary alcohol is reacted with a tertiary olefin in the presence of a zeolite having a silica to alumina mole ratio of at least 10 and the x-ray diffraction disclosed therein to provide a tertiary ether.
It is an object of the present invention to provide a process for converting low cost, readily available sources of light olefins to ether(s) which can be used as high octane blending stocks for gasoline.
It is another object of the invention to provide a process for catalytically converting olefin(s) in an olefin conversion unit to mixtures of alcohol(s) and ether(s) employing an acidic zeolite catalyst and thereafter recovering and recycling at least a portion of the product alcohol(s) to the olefin conversion unit to increase the overall yield of ether(s) therein.
It is a specific object of this invention to react a feed containing a substantial amount of propylene with water in an olefin conversion unit in the presence of an acidic large pore zeolite such as zeolite Beta to provide a mixture of IPA and DIPE and to recycle at least a portion of the IPA to the olefin conversion unit to increase the overall yield of DIPE.